1. Field of the Invention
The present invention relates to a recording tape cartridge which rotatably accommodates, within a case, a reel around which a recording tape, such as a magnetic tape or the like, is wound.
2. Description of the Related Art
Recording tapes such as magnetic tapes and the like are used as external recording media for computers and the like. Little space is required to accommodate such a recording tape at the time of storage thereof, and a large amount of information can be recorded thereon. A so-called single-reel recording tape cartridge is used in which a single reel, on which such recording tape is wound, is rotatably accommodated within a case.
In such a recording tape cartridge, a reel gear is provided in an annular form at an end surface of the hub of the reel around which the recording tape is wound. The reel gear is exposed from a gear opening of the case so as to be able to mesh with a driving gear of a drive device. When the recording tape is pulled-out from the case and used, the reel is positioned in the axial direction and rises up within the case, in a state in which the reel gear is meshed together with the driving gear. Driving force is transmitted to the reel due to the rotation of the driving gear, and the reel is driven to rotate.
The axial direction positioning of this reel is carried out by the meshing-together of the reel gear and the driving gear. Specifically, as shown in FIG. 13, the meshing surfaces of teeth 202 of a reel gear 200 and teeth 206 of a driving gear 204 are formed in taper shapes. The reel is positioned in the axial direction in a state in which the teeth 202 and the teeth 206 mesh together such that there is no backlash. Therefore, a reference plane D of the reel with respect to the axial direction within the drive device (i.e., when the reel is driven to rotate) is, for example, an imaginary plane which is the meshing pitch plane of the teeth 202 and the teeth 206. Further, the reel is driven to rotate in the rotating direction shown by the arrow R, in the state in which the teeth 202 and the teeth 206 are meshed together.
In such a recording tape cartridge, the dimensions of the respective portions are determined by using, as a reference, the reference plane D which is obtained by the reel gear 200 and the driving gear 204 meshing together. Therefore, high dimensional accuracy is required of the reel gear 200 and the driving gear 204. Further, because the reference plane D is formed in a state in which the large numbers of teeth 202 and 206 are meshing together, evaluation of the dimensional accuracy of the reel gear 200 and the driving gear 204 is difficult in spite of the fact that high accuracy is required of the reel gear 200 and the driving gear 204. Namely, for example, in a case such as when a given reel gear 200 and a given driving gear 204 do not mesh together correctly, it is difficult to ascertain whether the problem is at the reel gear 200 or the driving gear 204.
Thus, a structure has been considered in which a reference surface is provided at the hub end surface of the reel, separately from the reel gear, such that the reel gear does not participate in the reel positioning function. (See, for example, U.S. Pat. No. 6,273,352.) In this structure, three convex portions for reference project at uniform intervals in the circumferential direction from a portion, at an end surface of the hub, which portion is at a radial direction outer side of the reel gear which is formed in an annular form. The reel is positioned in the axial direction by reference surfaces, which are surfaces of the convex portions for reference which are orthogonal to the axis of the reel, being made to abut a positioning surface of a rotating shaft which has the driving gear at the drive device. In this way, by making surfaces which are orthogonal to the axis of the reel be the reference surfaces, control of the dimensions of the respective portions of the recording tape cartridge is easy. Note that, in this structure, the reel gear and the driving gear are structured so as to mesh together at taper surfaces in the same way as in the above-described structure. Backlash arises between the reel gear and the driving gear due to the positioning surface and the reference surfaces of the convex portions for reference abutting each other.
However, in this structure, there is room for improvement of the rigidity and the like of the convex portions for reference at the reel. Further, when attempts are made to make the backlash as small as possible, there is the concern that the reel gear and the driving gear will abut at the taper surfaces thereof before the reference surfaces and the positioning surface abut each other, and that the reel will not be positioned accurately in the axial direction.
Further, in the above-described respective structures, because the reel gear and the driving gear mesh together at taper surfaces, there is the concern that the torque of the driving gear will be converted, by the meshed-together surfaces, into thrust in the direction of making the reel gear and the driving gear move away from one another, and that the reel will joggle in the axial direction. If the reel joggles, the recording tape wound around the hub of the reel will be drawn-out or rewound while meandering, and therefore, recording or playback of the information of the recording tape will be adversely affected.